The present invention relates to an operating method for a cooling device for cooling a metal strip by means of a liquid coolant,                wherein the cooling device has an application device, by means of which coolant is applied to the metal strip,        wherein the coolant is fed to the application device by a feed line,        wherein a valve device is arranged in the feed line,        wherein an upstream condition detection device is arranged upstream of the valve device in the feed line and is used to detect an upstream condition of the coolant that the coolant has in the feed line upstream of the valve device,        wherein a control device sets the valve device.        
The present invention also relates to a computer program which comprises machine code that can be executed directly by a control device for a cooling device for cooling a metal strip by means of a liquid coolant,                wherein the execution of the machine code by the control device has the effect that the control device determines                    on the basis of a setpoint value for a coolant flow of the liquid coolant that is to be applied per unit of time to the metal strip by means of an application device,            an upstream condition of the coolant that the coolant in a feed line for the liquid coolant has upstream of a valve device arranged in the feed line, and            a valve characteristic of the valve devicea setpoint activation of the valve device, and correspondingly activates the valve device,                        wherein the liquid coolant of the application device is fed by the feed line.        
The present invention also relates to a control device for a cooling device for cooling a metal strip by means of a liquid coolant, wherein the control device is formed as a software-programmable control device and is programmed with such a computer program.
The present invention also relates to a cooling device for cooling a metal strip by means of a liquid coolant,                wherein the cooling device has an application device, which applies the coolant to the metal strip,        wherein the coolant is fed to the application device by a feed line,        wherein a valve device is arranged in the feed line,        wherein a coolant flow that is applied per unit of time to the metal strip by the application device is set by setting the valve device,        wherein an upstream condition detection device is arranged upstream of the valve device in the feed line and is used to detect an upstream condition of the coolant that the coolant has in the feed line upstream of the valve device,        wherein the cooling device has such a control device.        
The aforementioned subjects are known for example from DE 10 2007 046 279 A1. In the case of DE 10 2007 046 279 A1, the valve device is formed as a switching valve, which is switched in a binary manner between the states of fully open and fully closed. The valve characteristic comprises a switching-on delay, a switching-off delay and an average coolant flow rate.
DD 213 853 discloses an operating method for a cooling device for cooling a metal strip by a liquid coolant, wherein the coupling device has an application device which applies coolant to the metal strip. The coolant is fed to the cooling device by a feed line. A valve device is arranged in the feed line. By setting the valve device to a respective open position, a coolant flow that is applied per unit of time to the metal strip by the application device can be set in a number of steps. A flowmeter is arranged upstream of the valve device in the feed line and is used to detect the flow through the valve device. A control device of the cooling device compares the detected actual value of the coolant flow with a setpoint value for the coolant flow. In a way corresponding to the deviation, the opening position of the valve device is corrected in steps.
Power cooling—that is to say the intensive cooling of metal strip—is a novel cooling method for cooling a metal strip during hot rolling or directly thereafter. It serves the purpose of specifically setting the microstructure, and consequently the mechanical properties of the end product. In particular, steels known as AHSS (=advanced high-strength steels) require ever greater cooling intensity and cooling flexibility. These requirements are met by power cooling.
In the course of power cooling it is necessary to set the coolant flow, i.e. the amount of coolant that is applied per unit of time to the metal strip, precisely, reproducibly and dynamically. In the prior art, this is done by a flowmeter arranged in the feed line to the application device and the flow is controlled by means of the valve device. However, this procedure has several disadvantages. In particular, an overshooting often takes place in practice when setting a new setpoint value. A settling phase, up to when the new setpoint value is steadily maintained, is often relatively long. Furthermore, flowmeters are relatively expensive.